Perfluoroalkyl carboxylic acids (PFCAs), or perfluorocarboxylic acids are compounds of the formula CnF(2n+1)CO2H that belong to the class of per- and polyfluoroalkyl substances. The simplest example is trifluoroacetic acid. These compounds are organofluorine analogues of ordinary carboxylic acids, but they are stronger by several pKa units and they exhibit great hydrophobic character. Perfluoroalkyl dicarboxylic acids (PFdiCAs) are also known, e.g. C2F4(CO2H)2.
Applications
Trifluoroacetic acid is a widely employed acid, used for example in the synthesis of peptides. Its esters are useful in analytical chemistry.
Longer-chain perfluoroalkyl carboxylic acids, e.g. with five to nine carbons, are useful fluorosurfactants and emulsifiers used in the production of polytetrafluoroethylene (Teflon) and related fluoropolymers.
Production
These compounds are typically prepared by electrochemical fluorination of the carboxylic acid fluorides followed by hydrolysis:
- CnH(2n+1)COF + (2n+1) HF → CnF(2n+1)COF + (2n+1) H2
- CnF(2n+1)COF + H2O → CnF(2n+1)CO2H + HF
Environmental concerns
Long-chain PFCAs such as perfluorooctanoic acid (PFOA) are either banned or being under scrutiny because they are extremely persistent and bioaccumulative. Short-chain PFCAs (scPFCAs) are formed from atmospheric oxidation of fluorotelomer compounds and chlorofluorocarbon (CFC) replacements introduced as a result of the Montreal Protocol.
Side-chain fluorinated polymers (SCFPs), in which fluorotelomers are attached to a polymer backbone, may release fluorotelomer alcohols through hydrolysis. The latter are then degraded to PFCAs.
Common examples
| Name | Abbreviation | Molecular formula | Molecular weight (g/mol) | CAS No. |
|---|---|---|---|---|
| Trifluoroacetic acid | TFA | CF3COOH | 114.02 | 76-05-1 |
| Perfluoropropanoic acid | PFPrA | C2F5COOH | 164.03 | 422-64-0 |
| Perfluorobutanoic acid | PFBA | C3F7COOH | 214.04 | 375-22-4 |
| Perfluoropentanoic acid [de] | PFPeA | C4F9COOH | 264.05 | 2706-90-3 |
| Perfluorohexanoic acid | PFHxA | C5F11COOH | 314.05 | 307-24-4 |
| Perfluoroheptanoic acid [de] | PFHpA | C6F13COOH | 364.06 | 375-85-9 |
| Perfluorooctanoic acid | PFOA | C7F15COOH | 414.07 | 335-67-1 |
| Perfluorononanoic acid | PFNA | C8F17COOH | 464.08 | 375-95-1 |
| Perfluorodecanoic acid | PFDA | C9F19COOH | 514.08 | 335-76-2 |
| Perfluoroundecanoic acid [de] | PFUnDA | C10F21COOH | 564.09 | 2058-94-8 |
| Perfluorododecanoic acid [de] | PFDoDA | C11F23COOH | 614.10 | 307-55-1 |
| Perfluorotridecanoic acid [de] | PFTrDA | C12F25COOH | 664.10 | 72629-94-8 |
| Perfluorotetradecanoic acid [de] | PFTeDA | C13F27COOH | 714.11 | 376-06-7 |
See also
References
- ^ Siegemund G, Schwertfeger W, Feiring A, Smart B, Behr F, Vogel H, McKusick B (2002). "Fluorine Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH: a11_349. doi:10.1002/14356007.a11_349. ISBN 978-3-527-30673-2.
- McGrath M (14 May 2020). "Ozone layer: Concern grows over threat from replacement chemicals". BBC News. Retrieved 23 May 2024.
- Pickard HM, Criscitiello AS, Persaud D, Spencer C, Muir DC, Lehnherr I, et al. (28 May 2020). "Ice Core Record of Persistent Short‐Chain Fluorinated Alkyl Acids: Evidence of the Impact From Global Environmental Regulations". Geophysical Research Letters. 47 (10). doi:10.1029/2020GL087535.
- Synthesis Report on Understanding Side-Chain Fluorinated Polymers and Their Life Cycle (PDF). OECD Series on Risk Management. Vol. 73. Environment, Health and Safety, Environment Directorate, OECD. 2022.
- Letcher RJ, Chu S, Smyth SA (April 2020). "Side-chain fluorinated polymer surfactants in biosolids from wastewater treatment plants". Journal of Hazardous Materials. 388: 122044. doi:10.1016/j.jhazmat.2020.122044. PMID 31955025. S2CID 210830499.
- Brendel S, Fetter É, Staude C, Vierke L, Biegel-Engler A (2018-02-27). "Short-chain perfluoroalkyl acids: environmental concerns and a regulatory strategy under REACH". Environmental Sciences Europe. 30 (1): 9. doi:10.1186/s12302-018-0134-4. PMC 5834591. PMID 29527446.
Further reading
- "Chapter 2: Perfluoroalkyl carboxylic (a) and dicarboxylic (b) acids". Fact Cards of Major Groups of Per- and Polyfluoroalkyl Substances (PFASs). OECD Environment, Health and Safety Publications Series on Risk Management. Vol. 68. The Organisation for Economic Co-operation and Development (OECD). January 2022. pp. 16–32.
- Guo Z, Liu X, Krebs KA, Roache NF (March 2009). "Perfluorocarboxylic acid content in 116 articles of commerce". Research Triangle Park, NC: US Environmental Protection Agency.